Modeling the disequilibrium species for Jupiter and Saturn: Implications for Juno and Saturn entry probe

TL;DR

This paper develops a diffusion-kinetics model to predict disequilibrium species in Jupiter and Saturn's atmospheres, aiding interpretation of upcoming measurements from Juno and Saturn entry probes.

Contribution

It introduces an updated diffusion-kinetics code with new thermodynamic and kinetic data, and proposes new chemical pathways for key disequilibrium species in giant planet atmospheres.

Findings

Identified C₂H₆ as a useful tracer for eddy diffusion.

Suggested new pathways for PH₃, SiH₄, GeH₄, and AsH₃ destruction.

Quantified discrepancies in CO kinetics from different reaction networks.

Abstract

Disequilibrium species have been used previously to probe the deep water abundances and the eddy diffusion coefficient for giant planets. In this paper, we present a diffusion-kinetics code that predicts the abundances of disequilibrium species in the tropospheres of Jupiter and Saturn with updated thermodynamic and kinetic data. The dependence on the deep water abundance and the eddy diffusion coefficient is investigated. We quantified the disagreements in CO kinetics that comes from using different reaction networks and identified C$_2$H$_6$ as a useful tracer for the eddy diffusion coefficient. We first apply a H/P/O reaction network to Jupiter and Saturn's atmospheres and suggest a new PH$_3$ destruction pathway. New chemical pathways for SiH$_4$ and GeH$_4$ destruction are also suggested, and another AsH$_3$ destruction pathway is investigated thanks to new thermodynamic and kinetic data. These new models should enhance the interpretation of the measurement of disequilibrium species by JIRAM on board Juno and allow disentangling between methods for constraining the Saturn's deep water abundance with the Saturn entry probes envisaged by NASA or ESA.